Conventionally, it is known that processes for producing a metal film encompass, for example, vapor deposition, sputtering, and ion plating which are called dry processing, and electrolytic plating and electroless plating which are called wet processing. The dry processing requires expensive equipment, and the wet processing has difficulty in forming a metal film which has a thickness of tens of nanometers to hundreds of nanometers.
In view of the problem, a technique is disclosed in which, after a cation-exchange group is generated by modifying a polyimide resin, a metal ion is fixed to the cation-exchange group, and then the metal ion is reduced, whereby a metal film is formed (see Patent Literature 1).    Patent Literature 1
Japanese Patent Application Publication, Tokukai, No. 2001-73159 A (Publication Date: Mar. 21, 2001)